This study provides preliminary psychometric support for a version of the Clinician-Administered Posttraumatic Stress Disorder (PTSD) Scale (CAPS; D. D. Blake et al., 1990) adapted for use with patients with schizophrenia (CAPS-S; J. S. Gearon. S. Thomas-Lohrman, & A. S. Bellack, 2001). Nineteen women with schizophrenia and co-occurring illicit drug use disorders were administered the CAPS-S, the Structured Clinical Interview for DSM-IV diagnoses (SCID). and scales measuring trauma-related psychopathology. The results indicate that the CAPS-S can distinguish between those with and without PTSD and that the symptom clusters measure unified constructs. Interrater and test-retest reliability were high for PTSD diagnosis and symptom clusters. Solid convergent validity was demonstrated between the CAPS-S and SCID-based PTSD diagnoses and the Impact of Event Scale. There is also preliminary evidence of discriminant validity. These results support the use of the CAPS-S in women with schizophrenia.